1. Field of the Invention
This invention relates to stepped-piston, internal-combustion engines having one or more cylinders each containing a stepped piston having a pumping part of larger diameter and a working part of smaller diameter, the working part of the piston being slidable in a working part of the cylinder and the pumping part of the piston being slidable in a pumping part of the cylinder. Combustion of fuel and air mixture takes place in the working part of each cylinder. Inlet ports (hereinafter referred to as "working inlet ports") are provided in the wall of the working part of the or each cylinder. At least one pump port is provided in the pumping part of the or each cylinder to enable a fresh charge to be induced into said pumping part and transferred from the pumping part to a receiver. The charge then passes from the receiver to the working inlet ports. The or each piston is connected to a crankshaft by connecting rods or other means for converting reciprocating motion into rotary motion. Such an engine is hereinafter referred to as "an engine of the kind specified". The charge introduced into the working part of the or each cylinder will be air only if the engine is a compression-ignition engine and a fuel-air mixture if the engine is a spark-ignition engine.
2. Description of the Prior Art
A number of prior proposals have been made for engines of the kind specified. An example of such a proposal is that described in GB-A-190,757. One embodiment described includes two cylinders in separate cylinder blocks having a common receiver which is provided in a member separate from the cylinder blocks and located between the two blocks and connected to the tops of the cylinders by pipes. A single rotary valve is employed to control the inlet of charge into the pumping part of each of the two cylinders and also to control the transfer of the charge from each pumping part into the common receiver. Inside the common receiver is a sleeve valve which is reciprocated by a connecting rod connected to the rotary valve and which is arranged to open ports in the wall of the receiver at the appropriate times to permit charge which has been pumped into the receiver by the pumping parts of the cylinders to be discharged down the pipes from the receiver into the tops of the working parts of the cylinders. A single cylinder version of the engine is also described.
GB-A-190,757 was applied for in 1921 and is a construction which is suitable for slow running two-stroke engines. In this arrangement the receiver is completely separate from the cylinder blocks, is of comparatively small volume having to fit between and to one side of the two cylinder blocks and the charge from the receiver into the cylinders is controlled by the sleeve valve mentioned above which is expensive and complicated. The arrangement described would not be suitable for high speed, two-stroke engines for modern automotive use.